While data is stored via localstorage someone who has access to the device could access the data by going to the rhythmisch.com. To circumvent this maybe it would be helpful to be encrypt the data and possibly require authorization as an optional setting.
A few ideas:
Use Face ID and Touch ID authentication built into safari (link)
Encrypt the data using a user password and salt. Not sure how long the session should last.
Check how other offline & local storage handle this
While data is stored via localstorage someone who has access to the device could access the data by going to the rhythmisch.com. To circumvent this maybe it would be helpful to be encrypt the data and possibly require authorization as an optional setting.
A few ideas: